Re: Computer-Simulated HPGe Gamma-Ray Spectra-Fission gases

[Andy Hull <hull@mail.sep.bnl.gov>]

Why not trap the iodine and run a spectrum on the collecting medium?
Charcoal has a lot of pore space, so that the fission gases may still
interfere. If memory serves me correctly, some years ago Carl Distenfeld
when he was at BNL developed a silver loaded silica gel which had a much
lower gas collection efficiency. Silver Zeolite also has a lower gas
collection efficiency than charcoal. I don't have a catalog at hand, but I
think that one or the other or both are commercially available.


At 02:10 AM 7/4/98 -0500, you wrote:
>The answer is quite specific to the age of the fission products [i.e. the
Xenon 
>composition and the Iodine composition], the detector type, and the sample 
>geometry.   So, "real spectra" but from other systems, may not represent the 
>situation on your system.  But, based upon TMI experiences measuring similar 
>ratios, I suspect you can see I-131, even in the presence of 1000x the 
>concentration of Xe133/135.  You may not be happy with the MDA, however.  
>
>There is a simple code, SYNTH, that generates spectra for a somewhat
generic Ge 
>detector and for a simple cylindrical source geometry. I think I have one of 
>the few legitimate copies of it.  I don't know if it is available any more.  
>But, if you will fully describe the sample-detector geometry, the Ge
detector 
>efficiency, diameter, and thickness, the radionuclides that are present, and 
>the concentrations of each of those nuclides, I will be happy to generate
the 
>spectrum for you.  But, while it makes  a pretty picture, there is little
data 
>validating the accuracy of the results.  It may or may not be sufficient;
you 
>will have to decide.
>
>We have much experience designing complex Ge spectroscopy systems with more 
>accurate computer codes.  We normally use MCNP to perform primary efficiency 
>calibrations of complex sample-detector geometries, such as this.  We have
much 
>data validating this process.  We also use MCNP to generate the primary 
>detector response characteristics for our ISOCS product, which the user
uses to 
>do efficiency calibrations on devices such as this;  but ISOCS doesn't
generate 
>spectra.  The input for the MCNP model requires an exact knowledge of the 
>source, the detector internals, and everything in-between the source and the 
>detector.  To generate full and accurate spectra, including the low energy 
>scatter from higher energy nuclides, requires much more modeling.
Everything 
>that causes scatter [e.g. things behind the sample] must be included in the 
>model, and the computer time is much longer, as some of the computer
tricks to 
>reduce computation time are no longer valid.   So, we must charge for that 
>service.    
>
>Please contact me if you want more details.
>
>Frazier Bronson  CHP
>Canberra
>Meriden, CT
>203-639-2345
>
>
>YOU WROTE:
>
>The Illinois Department of Nuclear Safety, would like to obtain HPGe 
>gamma-ray spectras of fission product gases with different fractions of 
>iodines and noble gases.  We are interested in learning, whether or not 
>iodines can be resolved in the presents of fission product nobles gases, 
>1000 times the quantity of the iodines.
>
>If you are willing to contribute a real spectra or know of a 
>computer code that can model HPGe gamma-ray spectra, your help would be 
>appreciated.
>
>Melanie Caspary
>Illinois Department of Nuclear Safety
>caspary@idns.state.il.us
>tel: 217-786-6366 
>fax: 217-786-7223
>
>